1. Field of the Invention
The present invention relates to an envelope measurement preprocessing circuit, and more particularly to an envelope measurement preprocessing circuit for converting a high frequency signal reproduced from a reproducer to a low frequency signal to thereby facilitate automatic measurement of the degree of flatness of a signal envelope.
2. Description of the Prior Art
Generally, in order to check an envelope state of a predetermined signal of a reproducer (by way of example, a video tape recorder (VTR)) which picks up and reproduces a data recorded on a recording medium, a user previously visually checked the signal using an oscilloscope or a programmable oscilloscope to thereby perform a sampling on the signal. In this way, the envelope of a signal waveform can be measured from the displayed data.
A conventional checking method of the envelope state thus described has drawbacks in that, firstly, an operational speed is slow and the operation is inaccurate due to the visual measurement. Secondly, a data sampling for measurement of waveform envelope is expensive due to the use of a digital oscilloscope. Thirdly, in a case where a signal necessary for the envelope check has a high frequency and the period thereof is long (by way of example, the frequency in the case of a signal used for an envelope check of VTR ranges, i.e., in the mega-hertz with a period of approximately 30 Hz) sampling must be performed with one period of a waveform divided into several parts due to a scope analysis capacity and, at the same time, a first trigger signal of each interval must adequately generated.